Surface enhanced Raman Scattering is a surface sensitive technique relating to a phenomenon that occurs when molecules are adsorbed onto suitably rough surfaces of noble metal having appropriate nanomorphologies. Noble metal nanostructures with uniform surface roughness are considered of high importance for the preparation of stable SERS substrates with high enhancement factors. In addition, other nanostructural features such as shape and homogeneous distribution of the metal nano-features throughout the substrate surface can be considered important requirements in the design of more analytically-sensitive and reliable SERS substrates. In this context, some approaches including self-assembled metal colloid monolayers and fractal-like colloidal aggregates of Ag nanoparticles possessing appropriate surface roughness have been conducted. Unfortunately, aggregates of the metal colloids tend to agglomerate, resulting in poor reproducibility of the SERS signals. This creates a major obstacle in the preparation of stable SERS substrates. While approaches based on templating or electron beam lithography techniques may be useful to generate specific metal nanostructures with desired morphologies, they require quite complex preparation methods and are not suitable for preparing efficient large-scale SERS substrates.
Regarding fabrication and development of these nanocomposites, it is desirable to restrict the nanoparticles to a small size regime (<100 nm) while maintaining a highly uniform dispersion of the nanocrystals, in order to exploit the unique properties of the metal nanocrystal networks. However, it is a conflicting process to simultaneously control the nanoparticle size while increasing the nanoparticle volume filling in the polymer matrix (i.e. packing density) due to the strong tendency of nanoparticles to agglomerate and form larger sized islands. A straightforward implementation of polymer-metal fractal nanocomposites for highly active SERS substrates for such applications has not yet been demonstrated.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.